ABSTRACT: Background: The goal of pertussis vaccination is protection, and immunologic memory and memory B cells are fundamental to the maintenance of long-term humoral immunity. While the correlates of protective immunity are not well understood, we hypothesize that the presence of vaccine antigen specific memory B cells in peripheral blood will be predictive of immunologic memory in the absence of detectable vaccine antigen specific antibody in sera. The R03 project will develop the tools, data and assumptions for future studies examining the role of memory B cells in the persistence of humoral immunity after Tdap immunization an will begin to investigate if reduced or absent specific memory B cells can be used as predictors of susceptibility to pertussis disease. Specific Aims: We will examine pertussis antigen-specific memory B cell responses to acellular pertussis (Tdap) vaccine and pertussis infection to determine the role of memory B cells in maintenance of durable protective immunity. Memory B cell responses will be measured in: (1) adults pre and post receipt of a Tdap booster, (2) adolescents after recently confirmed pertussis infection and adolescents after recent Tdap booster vaccine, and (3) adolescents 2, 5, 7 and 10 years after a prior pertussis infection, or 2 and 5 years after a Tdap booster. Methods: Enzyme-linked immunosorbent spot assay (ELISPOT) techniques will be used to measure the presence of memory B cells in peripheral blood mononuclear cells (PBMCs). The assays include the separation of PBMC from whole blood, the measurement of circulating antibody secreting cells (ASC) in PBMC by ELISPOT, the polyclonal stimulation of PBMCs and the assessment of antigen specific memory B cells responses by ELISPOT. We will recruit and enroll a small number of adult Tdap vaccinees, recent and historic adolescent laboratory confirmed pertussis cases and adolescent Tdap vaccinees. Adult vaccinees will be staff of Boston Medical Center. Adolescent vaccinees will be recruited from a pediatric practice. Confirmed cases will be obtained through collaboration with Massachusetts Department of Public Health through Dr. Loughlin's established Active Pertussis Surveillance Project. Outcome: Primary outcome is to calculate the proportion of participants with detectable antigen specific B cell derived ASC and to compare these proportions across time points within study populations, and across study populations at similar time points. PUBLIC HEALTH RELEVANCE: Defining the duration of protection conferred by Tdap vaccine will inform our vaccination strategies, specifically setting the timing for Tdap boosters. In this R03 application, the preliminary investigations aimed to determine if evidence exists of detectable memory B cell responses after infection or immunization. The conclusions from this study could lead to future research projects to monitor the role of memory B cells in the maintenance of humoral immunity post Tdap, and specifically to investigate the role of vaccine antigen specific memory B cells as a predictor of susceptibility to pertussis infection or disease.